Larger wheel diameter - slower acceleration

[VS 5.0]

I can't recall any quantifications, sorry … just that it's noticeable. What I'm talking about is not to do with unsprung weight, that affects handling but will hardly affect acceleration (unless it contributes to something like axle-tramp or other loss of traction); I'm talking about the change in ability to accelerate the wheels due to the mass being further from the centre.

OK try this if you're sitting in a chair that spins (at work or in a home office). Consider how little your hands/arms weigh compared to the rest of you. Spin the chair around with your arms held out, at a (safe) decent rate … then pull your arms in. You rotate faster, and noticeably faster. You've not changed the total mass involved, just pulled it in closer to the centre, and without any energy input the rate of rotation increased.
To accelerate your car, the diff has to increase the rate at which those wheels are turning; the further from the centre the mass is, the more energy it takes to increase the wheel's rate of rotation (and without spinning the wheels faster the car can't go faster).

Makes it clearer, thanks.

 

[Skylarking]

Yep, moment of inertia is the principle behind it all. The further the mass is from the rotational axis, the higher the moment of inertia becomes. A high moment of inertia just saps power when getting the engine and drive line up to speed and is why ice skaters start their spins with arms outstretched.

This is the basic principle that results in F1 clutches being so tiny that you can hold them in one hand. Because their weight is much closer to the rotational axis, they can be spun up very fast with more torque getting through the system... and for the same reason, F1 wheels are much small in diameter than what we have on our road cars. It all aids in accelerating the engine, gearbox shafts and wheels with the most amount of energy actually getting to the road.

End result is that, from a performance perspective, we’d all be better off with smaller diameter wheels and clutches. But small wheels don’t look as cool as 20” wheels and who sees the clutch other than a mechanic

 

[panhead]

Decreasing the unsprung weight makes a noticeable difference to handling.

Lightened rims and you can also purchase light tyres make a difference to acceleration from a standing start, I really notice the difference in the way my cars jump out of the hole when I swap back and forth for various reasons.

I’ve not ever notice any difference in acceleration whilst already in motion.





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[panhead]

You don't see too many very fast high end or hyper cars with high side wall tyres these days nor do you see them on V8 Supercars.

I think it comes down to how much you're prepared to spend, do you want the really good stuff that will actually make a difference or are you just after the look.

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[VS 5.0]

You don't see too many very fast high end or hyper cars with high side wall tyres these days nor do you see them on V8 Supercars.

Still greater sidewall than on my 20" tyres though.

And don't forget about those NASCAR balloons.

 

[Skylarking]

High sidewall tyres may help improve contact patch on acceleration but they’d be absolute crap at corners. This is why you don’t see high sidewall tyres in wiggly circuit racing...

But you can’t change physics, larger moment of inertia is no good. However, it wouldn’t help Holden sales if V8 supercars ran 12” diameter 12” wide rims since they don’t sell road cars with such rims (and they would look odd in this modern age of 20” and bigger rims that we are becoming used to).

And for the most, in road cars with fuel consumption issues aside, it is largely irrelevant as upping engine power to cater for bigger wheels is a no brainer. And manufacturers can charge more as higher power and bigger wheels which is what people want.

 

[426Cuda]

Still greater sidewall than on my 20" tyres though.

And don't forget about those NASCAR balloons.

Yes, but nascar isn't subject to as much tight cornering and directional change as touring cars / V8 supercars. They also have more power. So the bigger tyres would help with traction under acceleration and lateral grip at high speeds.

 

[VS 5.0]

So not a fan of this look then @Skylarking ?

 

[426Cuda]

So not a fan of this look then @Skylarking ?

Hahahaha

 

[VS 5.0]

but nascar isn't subject to as much tight cornering and directional change as touring cars / V8 supercars

Track dependant of course.